Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
The present disclosure relates to an image processing apparatus that performs color conversion and other image processes, a non-transitory computer-readable recording medium storing an image processing program, and an image process apparatus.
Typical image forming apparatuses, such as printers and multi-function peripherals (“MFPs”), use a pulse-surface-area modulation method or a pseudo modulation method (e.g. ordered dithering method, error diffusion method, or the like), in which a multi-valued color is artificially represented with a set of dots, to perform an image process.
In this image process, however, if the number of gradation steps is limited, for example, to improve stabilization or obtain a desired gradation curve, a visual discontinuity may occur in the image. This visual discontinuity may cause so-called “contouring” significantly reducing image quality.
To solve this problem of contouring, some technologies have been proposed. In an example of technology, to perform correction to improve gradation characteristics and prevent the occurrence of contouring, noise is added to a portion at which continuity is lost in input/output characteristics or a reference value in an error diffusion method is changed.
However, contouring has sometimes appeared around the perimeter of a color area during so-called gamut mapping, which is performed to correct a color area difference. In other words, contouring may appear when the same color value continues in a certain area. It has not been possible to prevent this contouring efficiently with the above technology.
The present disclosure relates to an image processing apparatus that prevents the occurrence of contouring by randomly performing fine modulation on tentative output color values obtained by color conversion without impairing image quality, a non-transitory computer-readable recording medium that has recorded an image processing program, and an image processing apparatus.